Fix link in doc
Fix link in doc

closes PLAT-5314
flag=none

Test plan:
* look in markdown file in gitiles to see that link is fixed

Change-Id: Ic13c6a9f35989a92dc70cc1f532fcf6339222d5e
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/224204
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
Reviewed-by: Weston Dransfield <e9203059795dc94e28a8831c65eb7869e818825e@instructure.com>
QA-Review: Weston Dransfield <e9203059795dc94e28a8831c65eb7869e818825e@instructure.com>
Product-Review: Evan Battaglia <e557ffdfc4b80aab44858030b0ae5370b86cb7b1@instructure.com>

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